1. Field of the Invention
The present invention relates to an adjustment mechanism for rotation runout and dynamic balance of a rotating tool.
2. Description of the Related Art
A spindle includes a spindle shaft to which a rotating tool is attached. In a machine tool, the rotating tool is generally attached to the spindle shaft using a collet chuck or a shrinkage fitting chuck. These chuck structures are subjected to little positional displacement, and the chucks have sufficient strengths.
In particular, spindles used for ultra-precision machining use an air bearing in order to reduce heat from and vibration in the bearing of the spindle shaft. The air bearing offers only low resistance to a heavy load, and thus, the bearing may be damaged when the spindle shaft is rotated at high speed with significant unbalance present. Thus, each time the balance is corrected, the rotation speed of the spindle shaft needs to be increased. The adjustment needs to be repeated until dynamic balance correction at the maximum operating rotation speed is finally completed. This is a time-consuming operation.
A conventional method for adjusting the dynamic balance will be described with reference to FIG. 16A and FIG. 16B.
A spindle 5 depicted in FIG. 16A includes a collet chuck (a tool holder 3 for the collet chuck) attached directly to a spindle shaft 4. Thus, the spindle 5 includes no mechanism adjusting runout of the tool. As depicted in FIG. 16A, when the dynamic balance is adjusted, a vibration sensor 63 and a rotation sensor 65 are attached to the spindle 5. Then, the spindle shaft 4 of the spindle 5 is rotated, and a dynamic balance measurement apparatus 61 is used to perform measurement.
The dynamic balance measurement apparatus 61 indicates how much weight should be added to which rotational phase. As depicted by arrow 67, the collet chuck (the tool holder 3 for the collet chuck) has 16 tap holes 35 formed in an end surface of the collet chuck at intervals of 22.5° and into which balance screws (not depicted in the drawings) are fitted in a threaded manner, as depicted in FIG. 16B. A balance screw (set screw) with a specified weight is placed in a tap hole closest to a phase specified by the dynamic balance measurement apparatus 61, to correct the balance. Thus, during the correction, the rotation of the spindle inevitably needs to be stopped.
Desirably, for rotating tools used for an ultra-precision machine, positional displacement in a direction orthogonal to the rotational axis is limited to 1 μm or less, and deviation of the dynamic balance during rotation is limited to 10 mg or less. The collet chuck and the shrinkage fitting chuck have structures unlikely to be displaced at the time of attachment but are not configured to be able to correct displacement. Furthermore, in the structures of these chucks, it is difficult to limit the positional displacement in the direction orthogonal to the rotational axis to 1 μm or less and to limit the deviation of the dynamic balance during rotation to 10 mg or less. The attachment of a weight for balance allows the dynamic balance to be manually adjusted but leads to the need to stop rotation of the spindle shaft each time the weight is attached. Automating the attachment and detachment of the weight is also difficult.